In a conventional vertical semiconductor device in which current is allowed to flow across a first main surface and a second main surface of a semiconductor substrate (semiconductor wafer), the semiconductor substrate has become increasingly more thinned film with the purpose of characteristic improvement (for example, on voltage reduction). On the other hand, in the field of high breakdown voltage semiconductor devices that control high voltages exceeding 1000V, it is necessary to become more thickened film according to breakdown voltage. That is, a semiconductor manufacturing apparatus will be increasingly required to process a plurality of semiconductor substrates having different thicknesses. In a wafer for ULSI, such as DRAM, the tendency to increase aperture is proceeding, and the tendency of film thinning to reduce costs is proceeding.
In a semiconductor substrate whose aperture is relatively as large as not less than 6 inches and whose thickness is relatively as thin as not more than 100 μm, its own low strength and bowing or fluxure most probably damage the semiconductor substrate in a semiconductor manufacturing apparatus or during transportation between semiconductor manufacturing apparatuses.
A conventional wafer carrier encases with a plurality of pieces (up to 25) of wafers raised vertically. Since this wafer carrier holds only the peripheral portions of wafers in order to minimize contact with the wafers surfaces, the holding area of the wafers is small. Between semiconductor manufacturing apparatuses or between buildings, this wafer carrier is usually transported as it is, but in some cases, transported with it encased in another case.
A resist coating process and a diffusion process will be described below as an example of processing treatment in a conventional semiconductor manufacturing apparatus.
In a resist coating processing apparatus, a wafer carrier with a wafer encased therein is set on a loader by a robot or manually. When a processing recipe is started, the wafer is taken out from the wafer carrier and transported solely to a position to perform pre-coating-bake and then subjected to pre-coating-bake. The wafer after being subjected to pre-coating-bake is transported solely to a position to perform coating and then subjected to coating. The wafer after being subjected to coating is transported solely to a position to perform post-coating-bake and then subjected to post-coating-bake. The wafer after being subjected to post-coating-bake is transported solely and then encased. The above operation is repeated 25 times to complete the processing of 25 wafers, so that the treated 25 wafers are encased in a wafer carrier set on an unloader. Thereafter, the wafer carrier is taken out from the unloader and transported to a processing treatment apparatus of the next step by a robot or manually.
In a diffusion processing apparatus having a diffusion furnace, a wafer carrier with a wafer encased therein is set on a loader by a robot or manually. When a processing recipe is started, the wafer is taken out from the wafer carrier and transported solely to a wafer encasing boat for holding and encasing wafers, and then arranged on the wafer encasing boat. The wafer encasing boat has a groove for holding a wafer. If the width of the groove is too large, there may arise, for example, the problem that a wafer inclines and contacts with the adjacent wafer especially when the wafer is processed in a vertical position within a horizontal diffusion furnace. To prevent such a problem, a groove having a width corresponding to the thickness of the treated wafer is formed in the wafer encasing boat. The wafer encasing boat with a desired wafer encased therein is transported into the furnace. Within the furnace, diffusion is performed with a desired technique such as oxidation and annealing. Upon the completion of diffusion, the wafer encasing boat is transported to the exterior of the furnace. After cooling the wafer encasing boat and the wafer for a predetermined period of time, the wafer is taken out from the wafer encasing boat and transported solely to the wafer carrier and then encased. Thereafter, the wafer carrier is taken out from the unloader and transported to a processing treatment apparatus of the next step by a robot or manually.
Since the foregoing treatments have been performed in the conventional semiconductor manufacturing apparatus, thin wafers and the like that are low in strength have the problem that they might be damaged or deformed during transportation.
Further, when using a plurality of wafers having different thicknesses, there has been the problem that a different processing may become a necessity in a jig or the like depending on the thickness of a wafer, thus complicating the treatment.
Patent document 1 discloses an example of a wafer transporting and storing method and an example of a wafer carrier, which transport and store with one wafer encased in a flat casing. Patent document 2 discloses an example of a wafer protecting case in which each wafer is encased so as to cover the entire periphery of the wafer.    Patent document 1: Japanese Patent Application Laid-Open Publication No. 5-246508    Patent document 2: Japanese Patent Application Laid-Open Publication No. 2002-237516
However, because the wafer carrier disclosed in Patent document 1 is shaped like a case, there has been the problem that the encasement and takeout of a wafer or the like requires the operations of opening and closing a cover of the wafer carrier, thus complicating the operation.
Also in the wafer protection case disclosed in Patent document 2, there has been the problem that the encasement and takeout of a wafer or the like requires the operations of opening and closing or the like, thus complicating the operation.